Removing incrustations from lead anodes used for chromium plating



Patented Dec. 14, 1948 REMOVING INCRUSTATIONS FROM LEAD ANODES USED FORCHROMIUM PLATIN G .lacob Hyner, Waterbury, Conn.,

assignor to United Chromium, Incorporated, New York, N. Y., acorporation of Delaware No Drawing. Application April 16, 1946, SerialNo. 662,617

1 Claim. i

This invention relates to the removing of incrustations from lead anodesused for chromium plating, and provides improvements therein.

Lead anodes (lead, but generally tin-lead, or antimony-lead) used inchromium plating solutions, in the course of operations, become heavilycoated with lead oxides (mainly PbOz) and also some lead chromate. Whenleft standing in a solution containing chromic acid, the anode becomescoated with lead chromate. These coatings act to partially insulate theanode, the coatings becoming thicker and more insulating with time. Thecoating interferes with the normal distribution of the chromiumdeposited on the cathode, and especially in industrial chromium plating,where such coated anodes are used as conforming anodes, seriousirregularities in current distribution and thickness of plate result.

Heretofore, coated lead anodes have usually had the incrustationsremoved by wire brushing. This procedure is lengthy, the coating oftenincompletely removed, and, because of the dust produced, isuncomfortable and dangerous to the operator. Removal of theincrustations by dipping in a solution of hydrochloric acid has alsobeen practiced, but is subject to the objection that it is difiicult toavoid introducing chloride radicals into the chromium plating solutionthereby upsetting the chromic acid-radical ratio of the plating baths.

The need for better ways of removing incrustations from lead anodes haslong been recognized.

The present invention provides a method of removing incrustations fromlead anodes, which is simple, safe, effective, quick, and without thedisadvantages of previous methods.

According to the present method, coated lead anodes are electrolyticallytreated, as cathodes, in an alkaline pyrophosphate solution.

The solution used is one of potassium pyrophosphate dissolved in water,about fifty grams of the pyrophosphate per liter being used. A greateror less concentration may be used. Sodium pyrophosphate may also beused.

The temperature may be from room temperature to boiling.

The voltage used is approximately 6 volts, between the coated lead anode(connected as cathode) and the anode of the cleaning bath. From thestandpoint of fast removal of the incrustations from the anodes, acurrent density of from 1 to 10 amperes per square inch is desirable. Onthe other hand, current densities as low as onetenth ampere per squareinch have been used.

The time of removal of the incrustation (cathodic action) varies withthe thickness of the coating on the lead anodes being removed. Mostanodes, including those heavily coated, can be satisfactorily cleaned infrom 1 to 20 minutes. When the current is first applied, slight gassingwill soon occur at sharp points and at edges; as the time of treatmentis extended the gassing will spread over all of the surface. When thegassing becomes uniform over the entire surface this is an indicationthat the electrolytic treatment is completed.

The lead anode which has been subjected to the cathodic treatment isthen removed from the solution and wiped while wet to remove a film ofloose, spongy material which is found on the lead anode after thecathodic treatment. Some of the lead is reduced from the coatings andremains on the anode as solid lead, and in recovering lead from thecoatings, as lead solidly attached to the anodes, there is a saving oflead (about onehalf), and this is an important advantage of the presentprocess.

The expression, lead anodes, in the claim, includes anodes of lead andalloys of lead used for anodes, such as, for example, antimony-lead andtin lead.

What is claimed is:

Amethod of removing incrustations from lead anodes used for chromiumplating such incrustations being mixtures of lead oxides and leadchromate, comprising suspending the lead article in an aqueous solutionconsisting essentially of an alkali-metal pyrophosphate, and passingcurrent to the aforesaid lead article, connected in circuit in saidsolution as a cathode, and cathodically reducing the incrusted mixtureof lead oxides and lead chromate to lead.

JACOB HYNER.

REFERENCES CITED The following references are of record in the fileofthis patent:

UNITED STATES PATENTS Number Name Date 923,864 Levy June 8, 19091,032,623 Reed July 16, 1912 1,918,159 Weisberg et a1 July 11, 1933OTHER REFERENCES Products Finishing, August 1941, pages 60, 61.

